Display apparatus having segmented integral regulator

ABSTRACT

These segmented-electrode gas panel displays include a plurality of groups of cathode electrodes arranged in a display matrix, each group having an anode electrode operably associated therewith, and an auxiliary voltage reference device formed within the display panel itself. The reference device comprises at least a pair of electrodes that are spaced apart and in contact with the same gas in the panel that is in contact with the display electrodes thereof. The regulator cathode is formed of multiple or segmented cathode elements or comprises several exposed portions of an electrode element that is masked by an apertured insulating layer. The display apparatus further includes circuit means coupled to the integral voltage reference device and to the display electrodes to regulate the bias on one set of them at a level which allows direct operation of the display panel by semiconductor integrated circuits which have limited output voltage signals available for energizing the display electrodes. Current in the regulator segments, if connected in common, will be automatically apportioned among them as a function of their glow-sustaining characteristics which provides improved regulation in the apparatus.

United States Patent Glaser -t 1 Jul 1, 1975 i 1 DISPLAY APPARATUSHAVING SEGMENTED INTEGRAL REGULATOR [57] ABSTRACT [75] Inventor:

[73] Assignee:

[22] Filed:

David Glaser, Green Brook. NJ.

Burroughs Corporation, Detroit, Mich.

June 20, 1974 Appl. No.: 481,029

[52] US. Cl. 340/336; 315/168; 315/169 TV;

340/343 [51] Int. Cl. G09f 9/32 [58] Field of Search 315/168, 169 R, 169TV,

315/147; 340/336, 324 R, 324 M, 343, 166 EL Primary ExaminerMarshall M.Curtis Attorney, Agent, or FirmPaul W. Fish; William B. Penn; Robert B.Green These segmented-electrode gas panel displays include a pluralityof groups of cathode electrodes arranged in a display matrix, each grouphaving an anode electrode operably associated therewith, and anauxiliary voltage reference device formed within the display panelitself. The reference device comprises at least a pair of electrodesthat are spaced apart and in contact with the same gas in the panel thatis in contact with the display electrodes thereof. The regulator cathodeis formed of multiple or segmented cathode elements or comprises severalexposed portions of an electrode element that is masked by an aperturedinsulating layer. The display apparatus further includes circuit meanscoupled to the integral voltage reference device and to the displayelectrodes to regulate the bias on one set of them at a level whichallows direct operation of the display panel by semiconductor integratedcircuits which have limited output voltage signals available forenergizing the display electrodes. Current in the regulator segments. ifconnected in common, will be automatically apportioned among them as afunction of their glow-sustaining characteristics which providesimproved regulation in the apparatus.

18 Claims, 14 Drawing Figures SHEET 1 l 1 I l 1 l l 1 l l 1 I 1 I R 52A4A ape 69A 9 FIG. 4

DISPLAY APPARATUS HAVING SEGMENTEI) INTEGRAL REGULATOR This applicationis related to Ser. No. 48l,l72 titled Multi-Position Character DisplayPanel Having Display Cathodes and Auxiliary Cathodes for Operating"filed June 20, I974 by James Y. Lee.

BACKGROUND OF THE INVENTION Various multiple electrode display devicesmay be adapted to operate according to the subject invention, includingsegmented-electrode displays such as the PANAPLEX panel display. Suchpanels include groups of cathode electrodes in the form of segments ofcharacters or symbols to be displayed, and each group has an associatedanode electrode. The cathodes of each group are selectively energizedtogether with each of the anodes at different times to display differentcharacters at the various display positions in the device.

Displays of this type are frequently used in digital devices andinstruments such as electronic calculators and the like which arepresently being widely marketed. In general, each type of calculatorrequires an associated circuit for driving the display device, whichpreferably is free of unnecessary complexity and is operable from apoorly regulated power supply. Also, it is usually desirable that itoperate such display devices from semiconductor integrated circuits andthe like which have limited output signal voltages and yet be tolerantof considerable variations in the ionization potential and the operatingpotential drop across such devices, for example.

Furthermore, it has previously been found to be necessary to blank orinterrupt the signals applied to such devices at the beginning or at theend of each display period to eliminate excited particles in the gas forpreventing spurious glow or cross-talk between adjacent displaypositions.

SUMMARY OF THE INVENTION An object of this invention is to permit theoperation of gas panel displays by a wide variety of low voltage logiccircuit modules such as semiconductor integrated circuits.

Another object of the invention is to permit operation of differentdisplay panels from unregulated power supplies.

Another object of the invention is to improve the sta bility of integralvoltage regulation in gas panel display systems.

According to a feature of the invention, the glow discharge on asegmented integral reference device can fully cover one or more portionsof its cathode at low current and provide a more stable referencevoltage than otherwise.

Other advantages and features of the invention are made clear in thefollowing description, with reference to the accompanying drawings,wherein:

FIG. I is an enlarged exploded view of a gas panel display with integralvoltage reference device,

FIG. 2 is an electrical schematic block diagram of a display apparatusincorporating integral voltage regulation,

FIG. 3 is an illustration of the electrical characteristics of a typicaldisplay panel in the invention,

FIG. 4 is a view ofa portion ofa panel showing a variation of theintegral regulator element,

FIG. 5 illustrates an anode waveform,

FIG. 6 shows an alternative connection of the integral reference device,and

FIGS. 7-14 illustrate various improvements in the structure of integralregulator cathodes, FIGS. 13 and 14 also showing associated anodeelements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A display panel with which theapparatus of the invention is usable is known as the PANAPLEX gas paneldisplay, such as is described and claimed in copending application Ser.No. l73,854, filed Aug. 23, I971. Briefly, the panel includes a baseplate 20, on which a plurality of groups of cathode segments 60A-G areformed by a silk screen process, with corresponding cathodes of eachgroup being connected to a conductive run 3OA-3OG as shown in FIG. 1.The arrangement of the parts is such that the runs and each of thecathodes are suitably insulated from the adjacent runs and theircathodes, as by layer 40 having front surface 42. One ofa plurality ofanode electrodes 90, is associated with each group of cathodes forselective electrical discharge with the individual cathode segments.Each anode preferably comprises a transparent conductive coating formedon the inner surface of the face plate of the panel. An ionizable gasatmosphere at a pressure suitable for sustained cathode glow dischargeis sealed in the panel between the plates.

Generally, in the operation of panel 10 in a calculator, the groups ofcathodes are energized in turn to display a numeral at each displayposition. This is accomplished by applying sets of negative-goinginformation signals which are spaced apart in time to the cathode runsand by applying positive-going signals to each of the anodes in order,and synchronous with, the cathode signals. As this scanning operation isrepeated at a suitable repetition rate, a series of apparentlystationary characters or symbols can be displayed by the panel.

According to the invention, auxiliary control elements are formed withinthe display panel as an integral voltage reference device. In FIG. 1,the voltage reference device comprises an anode 99 formed on the innersurface of face plate 100 and a cathode 7S disposed on the base platewithin the gas in the panel as the other electrodes. The referencedevice may be provided in the display envelope adjacent the first groupof cathodes 60 that are scanned, as shown, or one may be provided atboth ends of the panel, if desired.

This integral reference device provides a reference voltage at asustaining potential which is used in the circuit of FIG. 2 to regulatethe bias voltage that is maintained on the other anodes of the display.The anode 99 and cathode 75 of the integral reference device may be incontact with the same gas that is in contact with display cathodes 60,as shown, to serve as a source of excited particles therein to shortenionization delay in the panel. If not needed as a source of excited gasparticles in the display, however, the anodes and cathodes of theintegral reference device may be disposed in an envelope that isisolated from the display envelope. The gas about the reference elementsalso may be different than the display gas or may include differentadditives, and the reference elements may be formed of differentmaterials than the display elements and may be processed differently, ifdesired.

If the auxiliary regulator electrodes are formed of the same materialswith the same processing as display electrodes 60 and 90, however, theywill have electrical characteristics which are similar to those of thedisplay electrodes. Further, if the reference elements are disposed inthe same gas as the display electrodes at the same pressure and spacing,they may all have substantially the same electrical characteristics asrepresented by curve 130 of FIG. 3. The voltage across the referenceelements appears at point 129 on curve 130, and the operating point ofthe display elements is at point 131 on the curve. Thus, if theelectrical characteristic of the display segments shifts downward orupward toward dashed curves 128 or 132 due to variations inmanufacturing or processing, or as a result of operation, the potentialacross the reference elements will shift likewise. The reference elementthereby provides a means of adjusting the potential applied to thedisplay device in accordance with shifts in the electricalcharacteristics of the display elements thereof. The integral regulatorapparatus of the invention thus compensates for variations or shifts inthe operating characteristics within a display device or among differentdisplay devices.

In the circuit shown in FIG. 2, which embodies the invention, a displaypanel is illustrated schematically. The display panel includes aplurality of substantially identical groups of cathode segments of whichcorresponding elements are electrically interconnected by conductors A306. A plurality of substantially identical anodes 90 are provided, onefor each group of cathode elements. This panel is thus suited for use asa display unit in calculators, instruments or other readouts. Alsodisposed in the panel is a voltage reference device including anauxiliary cathode 75 and an auxiliary anode 99. Reference cathode 75 isshown grounded in the figure, but a resistance element may be connectedbetween it and ground for raising its potential when conducting, or itmay be connected to a source of negative potential to lower itspotential, if desired.

The cathode conductors 30A 30G are each connected to an output conductor205 of a source of data signals 300 and to a resistor 220, the other endof which is connected to ground. The cathode segments are thereby heldnear ground potential normally, and are switched negative by apredetermined voltage via conductors 205 when selected by data source300 for a display.

The anodes 90, associated with the groups of cathode elements, are eachconnected to one plate of a coupling capacitor 175 by a conductor 170.The other plate of each capacitor 175 is connected to an outputconductor 190 of sequencer 200 and to one end of a resistor 195. Theother ends of resistors 195 are connected to ground and hold conductorsI90 normally at ground potential. Sequence controller 200 selectivelyraises the potential on one of conductors 190 toward a positivepotential to address an anode 90. The associated capacitor 175 is pulledpositive thereby, and this rise in potential is coupled by the addressedcapacitor 175 to the corresponding anode 90 which it energizes toproduce a glow discharge at simultaneously energized ones of thecathodes.

The anode electrodes 90 are also each connected to the cathode of adiode 210, the anode of which is connected to a reverse-biased Zenerdiode 124 which is connected to the emitter of transistor 150, by bus125. The collector electrode of transistor 150 is connected to one endof resistor 155, the other end of which is connected to a positivevoltage supply terminal which may vary by :35 per cent or more, forexample. The base electrode of transistor 150 is connected to theauxiliary reference anode 99 by conductor 115 and is coupled to thepositive voltage supply terminal 165 by resistor 160.

Transistor 150 functions as the pass element of a regulator which biasesthe display anodes 90 sufficiently positive with respect to the displaycathodes so that relatively small signal voltage excursions on theanodes and cathodes will cause a glow discharge in the panel. Inoperation, a glow discharge between the auxiliary reference cathode 7Sand anode 99 is established by the voltage supply potential on terminal165, and resistor 160 presents a load represented by the steep R loadline on FIG. 3. This establishes a reference potential V across thereference device and a current I through it, based at the low point 129in the normal glow region on characteristic curve 130. As the referencecurrent I changes due to a change in the voltage supply potential, thereference voltage V changes relatively little at this point on thecurve.

This reference voltage V appears on anode 99 of the integral referencedevice and on the base electrode of regulator transistor 150 since thecathode of the reference device is at ground potential. The emitter oftransistor 150 follows this voltage and serves as a current source tocharge capacitors 175 through diodes 120, and Zener diode 124 whichsubtract from the reference voltage. Bus 125 is thereby maintained atseveral volts below reference voltage V and the anodes of the displaypanel 10 are biased at less than a volt below the potential on bias busthrough diodes 120. The amount that Zener diode 124 drops the biasvoltage on the anode electrodes below reference volt age V assures thata signal applied only to one of the anodes or to one or more of thecathodes will not cause a discharge in the panel. This bias voltage thatis maintained on anodes 90 by the integral reference device andtransistor permits the display to be operated by small voltage signals,and depends on the characteristics of the panel rather than the circuit.

The display electrode segments or elements 60 are customarily operatedin the abnormal glow region and the operating point 13] is determined bythe magnitude of reference voltage V minus the voltage drop of the Zenerdiode, and the cathode and anode signal voltages, which are additive.The sum of these voltages is represented by voltage V which is developedacross the display elements of the panel and causes current in thedisplay segments and the resultant level of glow discharge that isdesired. The difference between the bias on the anodes based onreference voltage V and the desired operating voltage V that ismaintained by this regulator, allows the signal voltages applied to thedisplay cathodes and to the anodes to be of suitably small amplitude forlow voltage semiconductor drivers and the like.

In the regulator circuit, each of the cathode runs 30A-30G is connectedto a separate conductor 205 which is coupled through a resistor 220 toground and is also connected to a source of information signals 300which may be embodied within an integrated circuit chip. An anode inputterminal 190 is connected to the junction of each capacitor and resistor195, and each terminal represents a connection to a control signalsource 200 which also may be portions of an integrated circuit module.

In operation of the circuit of FIG. 2, when the circuit is turned on,the voltage reference element fires, and transistor 150 conducts untilcapacitors 175 are charged through diodes 120 to the reference voltage Von each anode 90, at which time the transistor turns off. This providesa pre-bias voltage on each of the anode electrodes in the panel. Withthe anodes thus set at a pre-bias level, as signals are applied to thecathodes and to each anode in turn, only a relatively small signal pulseof the order of to 40 volts is required to energize each group ofcathode electrodes and each anode electrode, in turn.

The waveform of the signal which appears at each anode is shown in FIG.5. The waveform includes a rising portion while capacitors 175 are beingcharged and then a horizontal portion 305 during the delay time beforethe gas is ionized and firing takes place. The

curved falling portions 310-370 represent the conduction time of a groupof cathodes, curve 310 representing discharge by one cathode element,curve 370 representing discharge by all segments in a cathode group andthe curves for other combinations of cathode segments falling in betweenthose curves. The waveform includes a final vertical portion 400 whichextends below the initial level of the anode signal. During thisnegative-going portion 405 of the anode signal, transistor 150 conductsas a current source to recharge anode input capacitors I75 and toneutralize the remaining charge or plasma at the display position beingturned off. By proper choice of the value of capacitors 175, the currentat the end of each pulse is considerably less than the initial amountdue to the capacitors being discharged as indicated by curves 310-370.The low terminal current and the low signal voltages employed introducean effective blanking interval between adjacent digits, thus eliminatingthe need of specifically timed blanking or of extra circuit elements toprovide such blanking.

ln a modification of the regulator, Zener diode 124 is eliminated fromthe circuit so that anode bias bus 125 is connected directly to theemitter of transistor 150. The bias on the anode electrodes is thendetermined by reference voltage V minus the base-emitter drop intransistor I50 and the forward voltage drop of diodes 120. If this levelof bias voltageallows energized cathodes to discharge with unaddressedones of the anodes, then cathode 75 of the integral reference device maybe connected to a slightly negative potential terminal instead of toground. Such a connection will lower the bias voltage on anode99 of thereference device as well as on the other anodes 90 and thereby preventspurious discharges in the panel to unenergized anode electrodes.

Further, ifit is possible to raise the bias on the anodes withoutcausing extraneous or spurious glow in the panel, then the cathode 75 ofthe voltage reference device may be connected to a slightly positivepotential terminal. Alternatively, cathode 75 of the integral referencedevice may be coupled to ground through a resistor 72 and areverse-biased Zener diode 74, as shown in FIG. 6. Both of thesemodifications will raise the reference potential on anode 99 of theintegral reference device and on anode bias bus 125, thus allowing theuse of yet smaller anode and cathode input signal voltages.

It should be noted that anode 99 of the integral reference device may beconnected directly to a reference potential terminal such as terminal165, with reference cathode coupled to ground through a load, to providea reference voltage from cathode 75 for biasing display cathodes 60rather than anodes 90. Reference cathode 75 is then connected to thecontrol electrode of a regulator transistor or other element forcharging capacitors connected in series with display cathodes 60 ratherthan anodes and thereby biasing the display cathodes. The input signalsfor the cathodes are thus shifted through the coupling capacitors,superposed on the cathode bias, and the application of simultaneoussignals on the anodes results in glow discharges in the display.

It is usually desirable to operate the integral voltage reference deviceat or near the low point 129 in the normal glow region on characteristiccurve 130, for example. This may be done simply by connecting it inseries with a resistive load such as resistor to a volt' age supplyterminal as in FIG. 2. That point provides a relatively constantreference voltage V since the characteristic is nearly flat at thatpoint for reference current densities near I and it accomodatesincreases or decreases in the reference current with little change inthe reference voltage.

Under some circumstances, however, the characteristic of the integralreference device changes during operation so that the reference voltageprovided by it decreases. It appears that this change is especiallypronounced in display panels including mercury as an antisputteringagent. It is believed that reference cathode 75 operates at a lowertemperature than the display cathodes 60 and that mercury vapor or othersubstances condense or accumulate upon the reference cathode. This iscaused by the integral reference device being operated in the normalglow region at low current density I and the display cathodes 60 beingoperated in the abnormal glow region at the much higher current densityI Some of the mercury that condenses onto cathode 75 of the integralreference device is believed to amalgamate with it and in some casesform a binary alloy and thereby lower the work function of its surface.The cathode fall of the reference cathode is thereby decreased and thereference voltage available for biasing the display electrodes,consequently, also decreases. The accumulation of free mercury or othermaterial on the surface of reference cathode 75 also may lower the workfunction of the surface of the reference cathode.

It appears, however, that the material of low work function on thesurface of the reference cathode 75 is thermally unstable or evaporatesif operated at a sufficiently elevated temperature. Various solutions tothis problem are illustrated in the drawing. It has been discovered thata glow discharge at a sufficiently high current density can be sustainedon one or more of a plurality of discrete areas 75, 75, 275, 975 of asegmented or suitably masked reference cathode as those illustrated inFIGS. 1, 4 and FIGS. 7-14. These discrete areas or segments 75, 275, 975may be exposed portions of a common area of cathode material or may beindividual elements which are electrically connected together in common.It appears that total area of the discrete cathode areas 75, 275, 975should ideally approximate that of a display cathode segment 60. Thearea of the reference cathode may, however, be somewhat less than thatof a segment of a display cathode, or it may be considerably larger, ifdesired, since only a few of the discrete areas or portions of thereference cathode usually glow at a given time.

Specific embodiments of a segmented or discontinuous integral referencedevice are illustrated in the drawing. In FIG. 1, a segmented referencecathode 75 is shown as a block letter B comprising severalinterconnected discrete areas, and in FIG. 4, the integral referencecathode is shown as exposed areas 75' adjacent an exposed anode area 109situated on insulating surface 42 and masked by insulating layer 45C. InFIGS. 8, the reference cathode of the integral reference devicecomprises areas 275575 exposed through apertures in insulating layers245575, interconnected by conductive portions 200-500 and connected toconductors 270570, respectively.

In FIG. 9, the integral reference cathode is a closed circuitous region675 and, in FIG. 10, it comprises discontinuous portions 775 exposedbeneath apertures in insulating layers 645 and 745 and being connectedto conductors 670 and 770, respectively. In FIG. 11, the cathode 875 ofthe integral reference device is exposed and situated adjacent andparallel to associated anode 809, with corresponding connectors 870 and849, beneath insulating layer 845. In FIG. 12, the integral referencecathode comprises exposed discrete areas or segments 975 adjacent anassociated anode 909, and having corresponding connectors 970 and 949,situated beneath insulating layer 945 which masks them.

This glow discharge at increased current density on cathodes 75, 275,975 of a segmented integral reference device seems to drive off orprevent the accumulation of excess mercury or other material on it. Thereference voltage established by the integral reference device therebytends to stabilize at some level rather than continuing to decreasefurther with time, as before. A representation of the process involvingthe segmented reference device is illustrated in FIG. 3. One or a few ofthe reference cathode segments 75, 275, 975 begins to discharge after asuitable potential is applied to terminal I65 in FIG. 2, for example. Itthen begins to accumulate mercury on its surface and the voltage acrossit decreases from V at point 129 on characteristic curve 130 to point126 on characteristic curve 128 and then toward point 127 at voltage Von curve 128.

The voltage across the segmented integral reference device then tends toremain near V and the corresponding increased current through thereference device appears to drive off or prevent further coating orcontamination of the reference cathode. The cathode fall of the segmentsor discrete areas 75, 275, 975 of the integral reference cathode is thusprevented from decreasing any further. Also, if any non-glowing segment75, 275, 975 experiences a decrease in its work function below that ofthe segment(s) that are actively glowing, then some of the referencecurrent transfers to the lower work function segment and it will beginto glow instead of the reference segment of higher work function. Thisoccurs principally when the coating, contamination, or amalgam on thesurface of a reference cathode segment glowing in the abnormal glowregion becomes cleaned-up or dissipated during operation and the workfunction of its surface increases toward that of its principal material.The potential across the integral reference device thus hovers around orbetween points 129 and I26 on characteristic curves 130 and 128,respectively, the stability of the reference voltage developed acrossthe integral reference device is thereby improved considerably.

Also, it should be understood that it is not necessary that the integralvoltage reference device assume an electrical characteristic which isbelow that of the display electrodes of the device, such as curve 128.With a segmented cathode 75, 275, 975 of sufficient area, an integralvoltage reference device may exhibit a characteristic which is abovethat of the display electrodes, such as curve 132. The voltage whichappears across the integral reference device then will approach the lowpoint on curve 132 and will reach a point on a characteristic curve nearcurve 130, or between them, during operation. The voltage across theintegral refer ence device then will tend to stabilize at that level, aspreviously described, which is suitable for biasing the displayelectrodes of the device. Also, means such as Zener diode 124 in FIG. 2may be employed for dropping the potential that is used for biasing thedisplay electrodes below the reference voltage by a suitable amount, ifdesired.

Although the preferred embodiments of the invention have been describedin detail, it should be understood that this disclosure has been by wayof example only. Many modifications and variations of the invention arepossible in light of the above teachings. It is, therefore, to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically disclosed.

That which is claimed is:

l. A display device comprising a gas-filled envelope having a viewingwindow and an insulating base plate,

a plurality of groups of cathodes shaped in the form of segments ofdifferent characters to be displayed and disposed along the frontsurface of the base plate and having terminals extending out of theenvelope,

an anode electrode associated with each group of cathodes for selectivedischarge therewith and having terminals extending out of the envelope,

an integral voltage reference device comprising at least a plurality ofinterconnected discrete cathode elements and an anode electrodeassociated with the elements within the envelope, and

means connected to the electrodes of the reference device for receivinga current sufficient to sustain a discharge between one or several ofthe reference cathode elements and the associated anode electrode tomaintain thereby a stable reference voltage across the reference device.

2. The display device of claim I wherein the discrete cathode elementsof the integral voltage reference device'comprise individual portions ofa conductive layer exposed by apertures in an insulating masking layeradjacent the conductive layer.

3. The display device of claim I wherein the discrete cathode elementsof the integral voltage reference device comprise conductive elementswhich are smaller in area than the display cathode elements of thedisplay device for conducting at higher current density than occurs inthe display cathode elements themselves.

4. The display device of claim 1 wherein the discrete cathode elementsof the integral voltage reference device and the display cathodeelements of the display device are formed of common materials 5. Thedisplay device of claim 1 wherein the discrete cathode elements of theintegral reference device are situated in substantially the same gasatmosphere at substantially the same distance from the anode of thereference device as are the display cathode elements of the displaydevice from the associated electrodes.

6. The display device of claim 1 wherein the discrete cathode elementsof the integral voltage reference device are substantially equal in areaand are situated substantially equidistant from the associated anodeelectrode within the envelope of the display device.

7. Display apparatus comprising a display device including a pluralityof groups of cathode elements shaped in the form of segments ofdifferent characters to be displayed and situated in a gas-filledenvelope having a viewing window and electrode terminals outside theenvelope, an anode electrode associated with each group of cathodeelements for selective discharge therewith,

an integral voltage reference device comprising at least an anodeelectrode and a plurality of interconnected but separate portions of acathode electrode associated therewith, and

means for conducting a current through said integral reference devicecomprising resistance means connected in series with it between a pairof voltage supply terminals,

the current established in the integral voltage reference device beingsufficient to cause a glow discharge on one or more of the discreteportions of the reference cathode for maintaining a voltage across thereference device near the low voltage point in the normal glow dischargeregion thereof.

8. The display of claim 7 wherein the cathode electrode of the integralvoltage reference device comprises a conductive layer having separateportions which are exposed by apertures in an insulating masking layeradjacent the conductive layer.

9. The display apparatus of claim 7 wherein the separate butinterconnected portions of the cathode electrode of the integral voltagereference device are smaller in area than the display cathode elementsof the display device for conducting a higher current density thanoccurs in the display cathode elements themselves.

10. The display apparatus of claim 7 wherein the interconnected butseparate portions of the cathode electrode of the integral voltagereference device and the display cathode elements of the display deviceare formed of common material.

11. The display apparatus of claim 7 wherein the separate portions ofthe cathode electrode of the integral reference device are situated insubstantially the same gas atmosphere at substantially the same distancefrom the anode of the reference as are the display cathode elements ofthe display device from the associated anode electrodes.

12. The display apparatus of claim 7 wherein the interconnected portionsof the cathode electrode of the integral voltage reference device aresubstantially equidistant from the associated anode electrode within theenvelope of the display device.

13. A display device comprising a gas-filled envelope having a viewingwindow and an insulating base plate,

a plurality of groups of cathode elements shaped in the form of segmentsof different characters to be displayed and disposed along the frontsurface of the base plate, with terminals extending out of the envelope,1

an anode electrode associated with each group of cathode elements forselective discharge therewith and having terminals extending out of theenvelope,

an integral voltage reference device comprising at least an anodeelectrode and a cathode electrode associated with each other within aportion of the envelope, and

a pair of terminals for the integral reference device separate from theother electrodes for receiving a current sufficient to develop asustained discharge in the reference device for maintaining a referencevoltage across it independent of the state of the other electrodes.

14. Display apparatus comprising a display device including a pluralityof groups of cathode elements shaped in the form of segments ofdifferent characters to be displayed and situated in a gas-filledenvelope having a viewing window and electrode terminals outside theenvelope,

an anode electrode associated with each group of cathode elements forselective discharge therewith,

an integral voltage reference device comprising at least an anodeelectrode and an associated cathode electrode situated within a portionof said envelope and each having terminals extending out of theenvelope, and

voltage regulating means coupled between an electrode of the integralreference device and one set of the display electrodes to bias them at avoltage related to the potential across said reference device,

the other set of display electrodes and the other electrode of theintegral reference device each being electrically connected to a secondvoltage supply terminal.

15. Display apparatus comprising a display device including a pluralityof groups of cathode elements shaped in the form of segments ofdifferent characters to be displayed and situated in a gas-filledenvelope having a viewing window and electrode terminals outside theenvelope,

an anode electrode associated with each group of cathode elements forselective discharge therewith,

means for driving the display device having first and second sets ofterminals for providing data and digit address signals, respectively,

means for interconnecting corresponding ones of the cathode elements andfor electrically connecting them to the respective data signalterminals,

capacitive means for electrically coupling each of the anode electrodesto a different one of the digit address signal terminals, and

means for biasing the cathodes and anodes of the display device towardthe operating potential thereof,

16. The display apparatus of claim 15 wherein the display means for thecathodes and anodes of the display device comprise voltage regulatingmeans coupled to the anode electrodes and a voltage reference device andresistance means coupled between a voltage supply terminal and thecathode elements of the display device.

electrodes of the reference device for the voltage regulating means areformed within the envelope of the display device in substantially thesame gas atmosphere at substantially the same pressure in which thedisplay cathode elements of the device are situated.

1. A display device comprising a gas-filled envelope having a viewingwindow and an insulating base plate, a plurality of groups of cathodesshaped in the form of segmentS of different characters to be displayedand disposed along the front surface of the base plate and havingterminals extending out of the envelope, an anode electrode associatedwith each group of cathodes for selective discharge therewith and havingterminals extending out of the envelope, an integral voltage referencedevice comprising at least a plurality of interconnected discretecathode elements and an anode electrode associated with the elementswithin the envelope, and means connected to the electrodes of thereference device for receiving a current sufficient to sustain adischarge between one or several of the reference cathode elements andthe associated anode electrode to maintain thereby a stable referencevoltage across the reference device.
 2. The display device of claim 1wherein the discrete cathode elements of the integral voltage referencedevice comprise individual portions of a conductive layer exposed byapertures in an insulating masking layer adjacent the conductive layer.3. The display device of claim 1 wherein the discrete cathode elementsof the integral voltage reference device comprise conductive elementswhich are smaller in area than the display cathode elements of thedisplay device for conducting at higher current density than occurs inthe display cathode elements themselves.
 4. The display device of claim1 wherein the discrete cathode elements of the integral voltagereference device and the display cathode elements of the display deviceare formed of common materials.
 5. The display device of claim 1 whereinthe discrete cathode elements of the integral reference device aresituated in substantially the same gas atmosphere at substantially thesame distance from the anode of the reference device as are the displaycathode elements of the display device from the associated electrodes.6. The display device of claim 1 wherein the discrete cathode elementsof the integral voltage reference device are substantially equal in areaand are situated substantially equidistant from the associated anodeelectrode within the envelope of the display device.
 7. Displayapparatus comprising a display device including a plurality of groups ofcathode elements shaped in the form of segments of different charactersto be displayed and situated in a gas-filled envelope having a viewingwindow and electrode terminals outside the envelope, an anode electrodeassociated with each group of cathode elements for selective dischargetherewith, an integral voltage reference device comprising at least ananode electrode and a plurality of interconnected but separate portionsof a cathode electrode associated therewith, and means for conducting acurrent through said integral reference device comprising resistancemeans connected in series with it between a pair of voltage supplyterminals, the current established in the integral voltage referencedevice being sufficient to cause a glow discharge on one or more of thediscrete portions of the reference cathode for maintaining a voltageacross the reference device near the low voltage point in the normalglow discharge region thereof.
 8. The display of claim 7 wherein thecathode electrode of the integral voltage reference device comprises aconductive layer having separate portions which are exposed by aperturesin an insulating masking layer adjacent the conductive layer.
 9. Thedisplay apparatus of claim 7 wherein the separate but interconnectedportions of the cathode electrode of the integral voltage referencedevice are smaller in area than the display cathode elements of thedisplay device for conducting a higher current density than occurs inthe display cathode elements themselves.
 10. The display apparatus ofclaim 7 wherein the interconnected but separate portions of the cathodeelectrode of the integral voltage reference device and the displaycathode elements of the display device are formed of common material.11. The display apparatUs of claim 7 wherein the separate portions ofthe cathode electrode of the integral reference device are situated insubstantially the same gas atmosphere at substantially the same distancefrom the anode of the reference as are the display cathode elements ofthe display device from the associated anode electrodes.
 12. The displayapparatus of claim 7 wherein the interconnected portions of the cathodeelectrode of the integral voltage reference device are substantiallyequidistant from the associated anode electrode within the envelope ofthe display device.
 13. A display device comprising a gas-filledenvelope having a viewing window and an insulating base plate, aplurality of groups of cathode elements shaped in the form of segmentsof different characters to be displayed and disposed along the frontsurface of the base plate, with terminals extending out of the envelope,an anode electrode associated with each group of cathode elements forselective discharge therewith and having terminals extending out of theenvelope, an integral voltage reference device comprising at least ananode electrode and a cathode electrode associated with each otherwithin a portion of the envelope, and a pair of terminals for theintegral reference device separate from the other electrodes forreceiving a current sufficient to develop a sustained discharge in thereference device for maintaining a reference voltage across itindependent of the state of the other electrodes.
 14. Display apparatuscomprising a display device including a plurality of groups of cathodeelements shaped in the form of segments of different characters to bedisplayed and situated in a gas-filled envelope having a viewing windowand electrode terminals outside the envelope, an anode electrodeassociated with each group of cathode elements for selective dischargetherewith, an integral voltage reference device comprising at least ananode electrode and an associated cathode electrode situated within aportion of said envelope and each having terminals extending out of theenvelope, and voltage regulating means coupled between an electrode ofthe integral reference device and one set of the display electrodes tobias them at a voltage related to the potential across said referencedevice, the other set of display electrodes and the other electrode ofthe integral reference device each being electrically connected to asecond voltage supply terminal.
 15. Display apparatus comprising adisplay device including a plurality of groups of cathode elementsshaped in the form of segments of different characters to be displayedand situated in a gas-filled envelope having a viewing window andelectrode terminals outside the envelope, an anode electrode associatedwith each group of cathode elements for selective discharge therewith,means for driving the display device having first and second sets ofterminals for providing data and digit address signals, respectively,means for interconnecting corresponding ones of the cathode elements andfor electrically connecting them to the respective data signalterminals, capacitive means for electrically coupling each of the anodeelectrodes to a different one of the digit address signal terminals, andmeans for biasing the cathodes and anodes of the display device towardthe operating potential thereof.
 16. The display apparatus of claim 15wherein the display means for the cathodes and anodes of the displaydevice comprise voltage regulating means coupled to the anode electrodesand a voltage reference device and resistance means coupled between avoltage supply terminal and the cathode elements of the display device.17. The display apparatus of claim 16 wherein the reference device forthe voltage regulating means is integral with the display device withinthe common gas atmosphere in which the display cathode elements aresituated in the envelope of the device.
 18. The display apparatus ofclaim 16 wherein the electrodes of the reference device for the voltageregulating means are formed within the envelope of the display device insubstantially the same gas atmosphere at substantially the same pressurein which the display cathode elements of the device are situated.